Deep brain stimulation (DBS) is a surgical option for patients with Parkinson's disease, essential tremor, dystonia, and tremor due to multiple sclerosis. In a typical DBS procedure, a neurostimulation system is implanted into a brain of a patient to electrically stimulate a target site in the patient's brain. One example of a neurostimulation system is an Activa® system manufactured by Medtronic, Inc. of Minneapolis, Minn. The Activa® system includes a stimulation lead, a Soletra® implantable pulse generator, and an extension lead. One type of stimulation lead includes four thin, insulated, coiled wires terminating into four 1.5 mm electrodes at its distal end and terminating into a connector at its proximal end. The stimulation lead is housed within a polyurethane jacket such that the diameter of the stimulation lead is 1.27 mm. The stimulation lead typically comes in two lengths, 40 cm and 28 cm. The implantable pulse generator (IPG) provides electronic pulses to the electrodes at the distal end of the stimulation lead. The extension lead includes a mating connector at one end to connect to the connector at the distal end of the stimulation lead. The extension lead also includes a male plug connector that connects to a female connection port provided on the IPG. Typically, the extension lead has a length of about 51 cm.
In a typical surgical procedure to implant the neurostimulation system for DBS, the surgical procedure begins with placing a stereotactic headframe around a patient's head to keep the patient's head stationary. The stereotactic headframe also helps guide a surgeon in the placement of a lead used for neurostimulation. Next, the surgeon takes an image of the patient's brain using sophisticated imaging equipment, such as a computed tomography (CT) or magnetic resonance imaging (MRI), to map the brain and localize a target site within the brain. Once the surgeon maps the brain, a local anesthetic is given to the patient. The surgeon then makes a small incision approximately 4 cm long that provides an approximately 3 cm×3 cm opening in the patient's scalp. Next, the surgeon drills a 14 mm diameter burr hole into the patient's skull to provide access to the patient's brain in preparation for the implantation of the lead.
The surgeon then inserts a temporary recording stimulation lead into the target site of the brain to test the stimulation. The surgeon tests the stimulation to maximize symptom suppression and minimize side effects before placement of a permanent stimulation electrode lead. Once the surgeon determines the exact target site of the brain, the temporary stimulation lead is removed and the surgeon commences the process of inserting the permanent stimulation electrode lead (hereinafter “stimulation lead”). Using the stereotactic frame and a hydraulic drive, the stimulation lead is inserted through the burr hole in the patient's skull and implanted in the target site within the brain.
A burr hole lead anchoring device (hereinafter “burr hole device”) is then implanted to support and secure the stimulation lead. Burr hole devices are manufactured, for example, by Medtronic, Inc. of Minneapolis, Minn. (the “Medtronic burr hole device”) and Image-Guided Neurologics, Inc. of Melbourne, Fla. under the trade name NAVIGUS® (the “IGN burr hole device”). An example of a Medtronic burr hole device is shown and described in U.S. Pat. No. 6,044,304, which is hereby incorporated by reference in its entirety herein. An example of an IGN burr hole device is shown and described in U.S. Patent Publication No. 2002/0052610 published on May 2, 2002, which is hereby incorporated by reference in its entirety herein.
Illustrated in FIGS. 1A-1B is one embodiment of a Medtronic burr hole device 5 includes a burr hole base ring 10 having an upper flange portion 15 and a lower sleeve portion 20 extending from the upper flange portion 15. The base ring 10 also has circumferential ribs 25 disposed about the periphery of the lower sleeve portion 20 and a septum 30 contained within an aperture 35 of the base ring 10. The aperture 35 serves as the opening through which the stimulation lead extends. The base ring 10 may be secured to a skull portion of the brain through a press fit where the circumferential ribs 25 engage the side wall of the burr hole and the septum 30 accepts and secures the stimulation lead in a substantially fixed position relative to the brain. The base ring 10 may include one or more grooves 40 positioned along the upper flange portion 15 of the base ring 10 to accept the stimulation lead. A cap (not shown) may be configured to close the aperture 35 of the burr hole base ring 10, and includes an opening to permit the stimulation lead to exit the base ring 10 via one of the grooves 40 in the base ring 10.
Illustrated in FIG. 2 is one embodiment of a IGN burr hole device 200 that can include a base ring 210, a support clip 215, and a cap 220. The base ring 210 includes a flange portion 225 having an aperture 230 communicating with the burr hole and two mounting holes 235 for attachment to the patient's skull. The base ring 210 may be secured to a skull portion of the brain through the use of two titanium screws 240 inserted through the mounting holes 235 and screwed into the skull. The base ring 210 includes one or more grooves 245 positioned along the upper flange portion 225 of the base ring 210 to receive the stimulation lead and permit the stimulation lead to lie generally parallel to the skull surface. The support clip 215 includes a disk 250 coupled to a cam 255. The cam 255 rotates, with respect to the disk 250, about an axis perpendicular to the plane of the disk 250, to create and substantially close a lead receiving opening 260 in which the stimulation lead is either passed freely (when open) or secured (when closed). The support clip 215 snap-fits onto the base ring 210 in any rotational orientation. The cap 220 includes an opening 265 to permit the stimulation lead to exit the base ring 410 via one of the grooves 245 in the base ring 210 and snap-fits into the base ring 210.
Once the burr hole device is properly implanted, the patient is put under general anesthesia. The connector on the proximal end of the stimulation lead is then connected to the extension lead. The extension lead is passed under the skin of the scalp, neck, and shoulder to connect the stimulation lead to the IPG. Finally, a small incision is made near the clavicle, and the IPG is implanted subcutaneously.
Illustrated in FIGS. 3A-3B are a cross-sectional view and a plan view, respectively, of a stimulation lead L implanted in the brain of a patient using a prior art burr hole device. The stimulation lead L can be described as having three portions as shown in FIGS. 3A-3B: 1) a first portion, which extends from a target site 305 in the patient's brain 310 to the burr hole device 315 in the patient's skull 320, that is typically between about 5 cm to about 12 cm long (indicated as “L1”); 2) a second portion, which extends from approximately the burr hole device 315 in the patient's skull 320 to the extension lead 325 (indicated as “L2”), that is typically between about 5 cm and about 20 cm; and 3) a third portion that is the excess portion of the stimulation lead L (indicated as “L3”). The excess portion of the stimulation lead L can be defined as a length of lead greater than a required length of lead to connect the stimulation lead L to the extension lead, if present, or to the IPG if the extension lead is not present. In other words, the excess portion of the stimulation lead L is the extra slack remaining after the stimulation lead L and the burr hole device have been implanted. In a typical DBS procedure, the excess portion of the stimulation lead L may be as long as about 30 cm long when using the 40 cm stimulation lead or as long as about 13 cm long when using the 28 cm stimulation lead. To manage the excess portion of the stimulation lead L, the surgeon typically inserts the excess portion of the stimulation lead L under the scalp in a random fashion using his/her fingers or a medical instrument.
Likewise, during the surgical procedure, the length of the portion of the extension lead extending from the IPG in the patient to the connection to the stimulation lead L is between about 10 cm to about 51 cm. Therefore, an excess portion of the extension lead exists. The excess portion of the extension lead can be defined as a length of lead greater than a required length of lead to connect the extension lead to the stimulation lead L. To manage the excess portion of the extension lead, the surgeon typically routes the excess portion of the extension lead in a random fashion using his/her fingers or a medical instrument.
The random management of the excess portion of the stimulation lead L and/or the excess portion of the extension lead can present MRI safety concerns to a patient having an implanted neurostimulation system. One possible MRI safety issue that can exist with patients having implanted neurostimulation systems is excessive heating of the electrode contacts on the stimulation lead L when the patient undergoes an MRI procedure. While not wishing to be bound by theory, the mechanism that can be responsible for MRI-related heating of the electrode contacts of the lead L is the electric current induced in the lead wires by the RF and pulsed gradient magnetic fields created by the MRI system. The lead wire can essentially act as an “antenna” and the electric field accompanying the RF and magnetic fields can induce current in the lead wire. A portion of the induced current can pass through the electrode contacts into the surrounding tissue, resulting in heating of the tissue. The RF and pulsed gradient magnetic fields can also induce functional disruption of the operational aspects of the implanted devices.
Other potential concerns that can exist with the random management of the excess portion of the stimulation lead L and/or the excess portion of the extension lead include the absence of a standardized procedure to manage the excess lead and the difficulty in making revision surgery.